In the manufacture of copper-clad laminates, such as used for circuit boards in the electrical field, it has been the typical practice to buy coils of thin copper foil and to provide means to combine a layer onto one or both faces of a laminate board during the manufacturing procedure. For example, the foil may be bonded to a semicured prepreg sheet prior to cutting and stacking with other prepreg sheets in the heat treating and pressing steps. In another method, there may be the integrating and bonding of the metal foil layer onto the laminate board during the final heat treating and pressing steps. In any event, from the aspect of being able to handle thin metal foils, these prior conventional methods of effecting metal-clad laminates have required the use of metal foils that are thicker than might otherwise be required for electrical current conducting reasons. For instance, with copper foils, it has been found difficult to handle a foil that is thinner than about 0.0007 to 0.0012 inches in thickness, although relatively thin coatings, having a thickness of from only about 0.0002 inches to about 0.0004 inches, may well be used as a conductor for a laminate circuit board.
In addition, it has become known that a thin film of conductive metal may be applied to a metal carrier sheet and then transferred from the latter to a laminate board. For example, a thin copper coating on a stainless steel press plate (caul plate) can be transferred to the face of an epoxy or resin impregnated fiber glass laminate sheet, typically referred to as a prepreg sheet. By way of explanation, in laminate board manufacture, a plurality of prepreg sheets are stacked together and then pressed and heated in a final treating operation to produce a desired stage of curing and a resulting rigid form of laminate board. The number of sheets used will, of course, vary in accordance with the desired thickness for the finished laminate board. For conductive laminate board, copper and other conductive metal will be pressed and bonded to one or both faces of a stack of sheets to result in providing copper cladding to one face or to both faces of the finished laminate type circuit board. In any event, in the use of plated caul sheets, such as will result from the use of the continuous system of the present invention, a caul sheet with a thin removable metal coating on one side can be used on the top or bottom of a pressing operation to provide a film transfer to one face of a resulting laminate board. Also, a caul plate with depositions on both sides may well be used in the middle of a stack of prepreg sheets, along with a coated plate at the other face of a stack, such that copper coatings can be imparted to both sides of a laminate board.